Catalysis study for space shuttle vehicle thermal protection systems

Experimental results on the problem of reducing aerodynamic heating on space shuttle orbiter surfaces are presented. Data include: (1) development of a laboratory flow reactor technique for measuring gamma sub O and gamma sub N on candidate materials at surfaces, T sub w, in the nominal range 1000 to 2000, (2) measurements of gamma sub O and gamma sub N above 1000 K for both the glass coating of a reusable surface insulation material and the siliconized surface of a reinforced pyrolyzed plastic material, (3) measurement of the ablation behavior of the coated RPP material at T sub w is greater than or equal to 2150 K, (4) X-ray photoelectron spectral studies of the chemical constituents on these surfaces before and after dissociated gas exposure, (5) scanning electron micrograph examination of as-received and reacted specimens, and (6) development and exploitation of a method of predicting the aerodynamic heating consquences of these gamma sub O(T sub w) and gamma sub N(T sub w) measurements for critical locations on a radiation cooled orbiter vehicle

A Novel Laboratory Course on Advanced Chemical Engineering Experiments

The chemical engineering curriculum in the United States has trained generations of technical experts who have successfully optimized chemical processes and products once they entered the chemical industry. The U.S. chemical industry, however, has entered a critical stage in which it must be able to create new and differentiated value through technical innovations that arc essential for long-term survival. This innovation process will require new skills that go far beyond the traditional expertise for the optimization of tasks possessed by young chemical engineers. The innovators must be able to identify new opportunities, explore the boundaries of technology, evaluate critical issues, develop and implement technologies, and communicate effectively with scientists and engineers from other disciplines. Therefore, one of the most important educational tasks of a modern university, in combination with a strong theoretical foundation, is to challenge students in laboratory courses to think, explore, hypothesize, plan, solve, and evaluate. The typical sequence of laboratory skills development stops short of introducing young engineers to the most critical aspects of experimental work. Chemical engineers usually begin developing their laboratory skills in chemistry courses, where experiments are closely managed. At this early stage in their development, students follow detailed instructions and learn basic principles by observing the results. In the undergraduate engineering laboratory course (the unit operations lab ), students have more freedom in experimental design but still have well-defined objectives and manipulate equipment someone else has set up. It is rare, however, for undergraduate students to be taught how to create new experiments. It is also rare for undergraduate students, and hence beginning graduate students, to have an appreciation for the care, planning, design, and testing required to produce equipment that will give reliable and useful results. Even such simple issues as leak testing or adapting analytical devices to new tasks are outside most students* experience. Even more important is an absence of opportunities to learn how the lessons learned from the failure of an approach can be fed back into the empirical process to seed the finally successful idea. All these skills require more creative freedom than is usually allowed in a well-structured laboratory course. In the novel laboratory teaching approach described here, we try to provide students with a learning environment that allows them to develop advanced experimental skills that are necessary for success in research and development environments

An Overview of Recent Development in Composite Catalysts from Porous Materials for Various Reactions and Processes

Catalysts are important to the chemical industry and environmental remediation due to their effective conversion of one chemical into another. Among them, composite catalysts have attracted continuous attention during the past decades. Nowadays, composite catalysts are being used more and more to meet the practical catalytic performance requirements in the chemical industry of high activity, high selectivity and good stability. In this paper, we reviewed our recent work on development of composite catalysts, mainly focusing on the composite catalysts obtained from porous materials such as zeolites, mesoporous materials, carbon nanotubes (CNT), etc. Six types of porous composite catalysts are discussed, including amorphous oxide modified zeolite composite catalysts, zeolite composites prepared by co-crystallization or overgrowth, hierarchical porous catalysts, host-guest porous composites, inorganic and organic mesoporous composite catalysts, and polymer/CNT composite catalysts

Spectral reflectance properties of zeolites and remote sensing implications

The 0.3- to 26-μm reflectance spectra of a suite of 28 zeolites were measured and analyzed to derive spectral-compositional-structural relationships. Below ~7 μm, the spectra are largely dominated by absorption features associated with zeolitic water. At longer wavelengths, the spectra are dominated by absorption features associated with the aluminosilicate framework. The spectra exhibit a number of systematic variations which can be used for both structurl and compositional determinations. These include: (1) distinguishing different structural groups on the basis of wavelength position variations associated with absorption features in the 8.5- to 26-μm region that are related to differences in the structure of the aluminosilicate framework; (2) determining the major cation which is present (Ca, Na, K) and the associated electronic environment of the zeolitic water on the basis of how these cations hydrogen bond to the water molecules in the void spaces and consequently affect water-related absorption band positions, particularly in the 1.4, 1.9, and 2.0- to 2.5-μm regions; (3) determining the Al:(Al + Si) ratio and SCFM chemical index on the basis of absorption features in the 7- to 26-μm region which are most sensitive to these compositional variations; and (4) identifying ironbearing zeolites on the basis of absorption features in the 0.35- to 0.9-μm region. The wavelength position and number of H2O-associated absorption bands are sensitive to factors such as the type of major cation, degree of hydrogen bonding, and size of the void space, all of which are somewhat interrelated.This study was supported by a research grant from the Natural Sciences and Engineering Research Council of Canada, a contract from the Canadian Space Agency Space Science Program, a discretionary grant from the University of Winnipeg (to E.A.C.), and the Louise McBee Scholarship of the Georgia Association for Women in Education, University of Georgia (to P.M.A.).This study was supported by a research grant from the Natural Sciences and Engineering Research Council of Canada, a contract from the Canadian Space Agency Space Science Program, a discretionary grant from the University of Winnipeg (to E.A.C.), and the Louise McBee Scholarship of the Georgia Association for Women in Education, University of Georgia (to P.M.A.).https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2000JE00146

CO + H/sub 2/ reaction over nitrogen-modified iron catalysts. Quarterly technical progress report, January 1-March 31, 1984

We have found that the nitride catalysts lose substantial amounts of nitrogen during the initial minutes of Fischer-Tropsch synthesis. In order to further study the stability of these catalysts, we have concentrated on the decomposition of the nitride in hydrogen. In addition, we have prepared a range of epsilon-Fe/sub x/N (2 < x < 3) phases. The Moessbauer parameters from these phases will aid in the identification and fitting of the transient epsilon phases formed during the carburization of Xi-Fe/sub 2/N. Extremely rapid nitrogen loss has been observed from Xi-Fe/sub 2/N in H/sub 2/ at 523 K both in constant velocity Moessbauer and in transient mass spectrometer experiments. In order to study the phase change from Xi-Fe/sub 2/N to ..cap alpha..-Fe in more detail, the hydrogenation temperature was decreased to 473 K and intermediate samples were quenched in liquid nitrogen to lock in the phase distribution for subsequent Moessbauer study. The spectra show complete conversion to ..cap alpha..-Fe at or before 21 minutes at 473 K. The intermediate samples show evidence of an extremely sharp gradient; only a very small amount of ..gamma..' or epsilon phase is observed. Thus, a moving front model of the phase transformation appears to be appropriate. Mass spectroscopy of the hydrogenation of Xi-Fe/sub 2/N at 523 K showed similar behavior to that of both the ..gamma..' and epsilon phases, in which an active surface species and a slowly activating one were observed. The H/sub 2/ was replaced by D/sub 2/ in this experiment in order to observe partially hydrogenated surface species in the initial spike of ammonia. All NH/sub x/D/sub y/ (x + y = 3) species were observed in this spike, indicating extremely rapid surface H/D exchange with gaseous ammonia. The fragmentation pattern of NH/sub 3/ in the mass spectrometer was also determined and will be used to calculate initial NH/sub x/ surface contributions. 23 references, 3 figures, 3 tables

CO + H/sub 2/ reaction over nitrogen-modified iron catalysts. Quarterly technical progress report, October 1, 1983-December 30, 1983. [Denitriding of iron nitrides in both hydrogen and helium]

The synthesis of epsilon-Fe/sub 2.7/N is confirmed by Moessbauer spectroscopy. Carburization of epsilon-iron nitride for 2.5 hours in 3H/sub 2//CO at 523 K starts the formation of a bulk structure similar to that seen during ..gamma..'-iron nitride carburization. Reaction of ..gamma..'-Fe/sub 4/N in 3CO/H/sub 2/ synthesis gas at 523 K shows a better bulk stability than reaction in 3H/sub 2//CO. Kinetic analysis of the product distribution at the higher CO ratio confirms greater activity and selectivity maintainance. The kinetics of denitriding in both He and H/sub 2/ was studied with a mass spectrometer. Extremely rapid nitrogen loss was observed from both ..gamma..'-Fe/sub 4/N and epsilon-Fe/sub 2.7/N catalysts in H/sub 2/ at 523 K. In both cases a initial exposure to H/sub 2/ produced a significant amount of NH/sub 3/ which we ascribe to an active surface species. Hydrogenation of the bulk continued with a slow rise to a maximum about 90 seconds after the introduction of H/sub 2/. The denitriding activity of the epsilon-Fe/sub 2.7/N catalyst was significantly higher than that of the ..gamma..'-Fe/sub 4/N catalyst. In contrast, the denitriding rate of epsilon-Fe/sub 2.7/N in He was significantly slower than that in H/sub 2/ until high temperatures (773K) were reached. An overall activation energy of 41.5 kcal/mol was obtained for this process. Comparison of the denitriding rate of virgin epsilon-Fe/sub 2.7/N in H/sub 2/ with that of the same nitride after five minutes of carburization during the hydrocarbon synthesis reaction indicates large differences in the overall rate. The carburized nitride was some 300 times less active to bulk hydrogenation than the virgin catalyst, which is indicative of significant changes in the first few layers of the nitride during the initial minutes of the synthesis reaction. 17 references, 5 figures

XPS and Sem Characterization of Pan-Based Carbon Fibers Treated in Oxygen and Nitric Oxide Plasmas

ABSTRACTUnsized, type II carbon fibers were treated for 2 to 60 minutes in either an oxygen or nitric oxide gas plasma and were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS revealed plasma treatments increased both oxygen and nitrogen functionality on the fiber surface. O2 plasma treatments showed a progressive increase of fiber surface oxidation from alcohol to carboxyl species, increasing the total surface oxygen from 3 atomic % to 46% after 60 minutes. N(1s) spectra for these fibers showed a broad peak centered at ca. 400.4 eV with a shoulder at ca. 398.2 eV, which most likely is attributed to nitrogen remaining from the polyacrylonitrile (PAN) precursor material. NO treatments only increased the total surface oxygen to 33%, but introduced additional nitrogen species onto the fiber surface compared to O2 plasmas. N(ls) spectra for the NO plasma treated fibers showed, in addition to the two nitrogen species mentioned above, a higher binding energy peak at ca. 405.5 eV, which is assigned to -NO2 species. This peak increased to a maximum intensity after 5 minutes of treatment and then decreased upon further treatment, even though the total nitrogen intensity remained constant at approximately 6%. Subsequent increases in the two lower binding energy species at 400.4 eV and 398.2 eV suggest -NO2 surface species were reduced to species such as amides, nitriles, and amines. Reducing the NO plasma power levels from 25 Watts to 5 Watts resulted in the same three peaks in the N(ls) spectra but required 30 minutes for the -NO2 species to reach a maximum intensity. Scanning electron micrographs (x 10,000 magnification) of fibers treated up to 5 minutes revealed that plasma treatments did not significantly change surface morphology. Small bumps on the surface appeared after longer treatments as the plasma began etching the fiber surface, but even 60 minutes of treatment did not significantly alter the overall fiber diameters.</jats:p